With increasing popularity of mobile voice and data communication, there is an ever increasing demand for high-speed data communication. User equipment configured to connect to a communication network, e.g. smartphones, have advanced processing capabilities. For battery powered user equipments, power consumption is of significant importance in order to increase battery lifetime.
In legacy implementations, a search for a cell performed by a user equipment which moves out of coverage may consume considerable energy. When a user equipment moves out of coverage, in idle mode the user equipment will try to select another cell within the same radio access technology (RAT) network. If this is not successful, the user equipment will start to scan for other RAT network(s) and will determine whether the user equipment can register in the other RAT network(s). The rate at which these scans are performed may be altered, e.g. by reducing the rate over time. The network may not know that the user equipment is no longer pageable until a location update timer expires. The location update timer can be between 6 minutes and 24 hours, depending on network configuration.
Conventionally, user equipments will periodically scan supported frequencies, frequency bands and/or RAT technologies when out of coverage in order to try and obtain coverage. The speed at which the user equipment can find a cell to camp on comes at the expense of power consumption, when searching unsuccessfully. More frequent scanning decreases the time required for the user equipment to find a cell to camp on, but increases power consumption. When the time between searches is increased to reduce the power consumption, the user equipment will generally take longer to find coverage when it is available. When a user equipment is located at an edge of a cell, it may end up in a state in which it frequently scans supported frequencies, frequency bands and/or RAT technologies to find a cell to camp on, which increases power consumption. For illustration, when a user equipment repeatedly goes into and out of the coverage of a cell while being located at the edge of the cell, a reduction of the scan rate may not be efficient because the scan frequency timer may be reset frequently. Additionally or alternatively, a user equipment which is attached to a non-preferred RAT network may start scanning of the preferred RAT network in a too frequent manner. Such situations may lead to a high utilization of a radio and modem portion of the user equipment which may quickly drain the battery.
Some UE implementations may increase the time between searches the longer they are out of coverage in order to preserve battery. This can then result in the UE taking longer to find coverage when it is available. Depending on the UE implementation, UE might end up in a state that it scans quite frequently. This could be due to the UE is going in and out of the cell while being in the cell edge. In this case the scan frequency timer will be reset every time. It can also happen that the UE is attached to a non-preferred RAT and therefore starts scanning of the preferred RAT in a too frequent manner. These unwanted behaviours generate high utilization of the Radio and modem part, and will quickly drain the battery. On the other hand, there is a trade-off between too infrequent scanning and the increased power consumption. If the scanning is too infrequent the UE will be out of coverage even though there should be a cell to camp.